The present invention relates to highly conductive polymer thick film compositions containing selected thermoplastic polymers, a tertiary amine, and a conductive silver flake filler. 2. Description of the Prior Art
The circuit patterns for membrane touch switches are usually made from a thermoplastic polymer thick film (PTF) composition containing particles of a conductive material dispersed in a volatile organic solvent-resin medium. The uncured PTF composition is usually screen-printed in the desired circuiting Pattern onto a substrate which may be either made from a rigid or flexible material. The PTF composition is then cured or dried, normally by the application of heat, and the volatile organic solvent material in the solvent-resin component is driven off. The curing causes the bonding of cured resin system with the conductive particles, thus forming the electrically active pattern for the membrane touch switches.
Numerous thermoplastic PTF compositions have been made for this and other applications.
For example, U.S. Pat. No. 4,371,459, which issued to Nazarenko on Feb. 1, 1983, teaches a screen printable PTF composition useful for making membrane touch switches comprising:
(a) 70-90% by weight, basis total solids, of a conductive phase consisting essentially of finely divided particles of: PA1 (b) 30-10% by weight, basis total solids, of polymers consisting essentially of: PA1 (c) a volatile nonhydrocarbon polar solvent having a boiling range of 150.degree.-220.degree. C. PA1 (a) 30-80% by weight of finely divided metal particles (including silver flake) and PA1 (b) 70-20% by weight of an organic medium which is a solution of: PA1 (a) a silver pigment material; PA1 (b) a ferro alloy pigment material; PA1 (c) a binder resin selected from thermoplastic acrylic, vinyl, urethane, alkyl, polyester, hydrocarbon, fluoroelastomer and cellulosic resins, and thermosetting acrylic polyester epoxy, phenolic, urethane, and alkyl resins; and PA1 (d) organic solvent carrier. PA1 (a) silver particles; PA1 (b) a reactive resin mixture comprising a carboxylated vinyl resin and a moderate chain length epoxy dissolved in: PA1 (c) an organic solvent (e.g., ester alcohol). PA1 (a) 15-35 parts by weight of a selected cyanate ester compound; PA1 (b) 65-85 parts by weight of an electrically conductive powder, including silver powder; PA1 (c) 0.5-15 parts by weight of at least one acetylacetone compound; PA1 (d) optionally, a metal chelate compound; PA1 (e) optionally, thermosetting resins; PA1 (f) optionally, thermoplastic resins; PA1 (g) optionally, rubbers; PA1 (h) optionally, natural or synthetic inorganic materials; PA1 (i) optionally, organic solvents; PA1 (j) optionally, organic acids; PA1 (k) optionally, inorganic acids; PA1 (l) optionally, coupling agents; PA1 (m) optionally, flame retardants; PA1 (n) optionally, self-extinguishing agents; and PA1 (o) optionally, catalysts including tertiary amines such as N,N-dimethyl benzylamine, N,N-dimethylaniline, N,N-dimethyltoluidine, N,N-dimethyl-p-anisidine, p-halogen-N,N-dimethylaniline, 2-N-ethylanilino ethanol, tri-n-butylamine, pyridine, quinoline, N-methylvorpholine, triethanolamine, triethylenediamine, N,N,N',N'-tetramethylbutanediamine, and N-methylpiperidine. PA1 (a) silver particles; PA1 (b) a reactive resin matrix comprising: PA1 (c) at least one organic solvent. PA1 (a) silver particles; PA1 (b) a reactive resin system made from: PA1 (c) a mixture of a ketone solvent and an ester solvent. PA1 (a) from about 88 to about 93% by weight, after curing, silver flake having an average particle size of about 0 5 to about 50 microns; PA1 (b) about 7 to about 12% by weight vinyl chloridevinyl acetate copolymer, said copolymer having a number average molecular weight from about 14,000 to about 35,000 and containing no carboxylic acid groups; PA1 (c) a solvent (e.g., gamma butyolactone, acetone, or cyclohexane). PA1 (a) 80-85% silver flake having an average particle size from about 0.5 to about 50 microns; PA1 (b) a resin system consisting essentially of: PA1 (c) at least one organic solvent. PA1 (1) exhibit a relatively long shelf life at room temperature (requires no refrigeration); PA1 (2) require a low curing temperature and short curing times in a convection oven (i.e., no higher than 130.degree. for no longer than 60 minutes) so as to not adversely affect the substrate; PA1 (3) be very conductive (or have very low electrical resistivity i.e., less than 0.015 ohms/sq./mil); PA1 (4) be sufficiently flexible when cured to be applied to flexible substrate (or substrates which might flex during their operation); PA1 (5) have acceptably good adhesion to membrane touch switch substrate (e.g., polyester films) when cured; PA1 (6) be easily prepared; and PA1 (7) be inexpensively applied to a substrate and cured without needing a complicated procedure. PA1 (a) about 3-15 parts of at least one vinyl acetate/vinyl chloride/dicarboxylic acid multipolymer resin; PA1 (b) a second thermoplastic resin selected from the group consisting of: PA1 (c) about 0.05-1 parts of a tertiary amine; PA1 (d) an effective amount of at least one organic solvent capable of substantially dissolving (a), (b), and (c) ingredients; and PA1 (e) about 50-80 parts of silver flake. PA1 (1) providing a polymer thick film composition as defined above; PA1 (2) applying said composition to a substrate; and PA1 (3) thermally curing said composition on said substrate. PA1 (a) about 3-15 parts of at least one thermoplastic vinyl acetate/vinyl chloride/dicarboxylic acid multipolymer resin; PA1 (b) a second thermoplastic resin selected from the group consisting of: PA1 (c) about 0.05-1 parts of at least one tertiary amine; and PA1 (d) about 50-80 parts of silver flake.
(1) 50-95% by weight silver; and PA2 (2) 20-5% by weight a base metal (i.e. Al, Sn, or Ni or mixtures thereof); PA2 (1) 10-65% by weight of a multipolymer prepared by copolymerization of vinyl acetate, vinyl chloride, and 0.3-10% by weight of an ethylenically unsaturated dicarboxylic acid in which the weight ratio of vinyl chloride to vinyl acetate is from 3 to 8; and PA2 (2) 90-35% by weight of a linear aromatic polyester resin having an intrinsic viscosity of 0.5 to 1 dissolved in PA2 (1) a linear aromatic polyester resin having an intrinsic viscosity of 0.5 to 1 completely dissolved in PA2 (2) a volative nonhydrocarbon solvent having a boiling point of 150.degree.-220.degree. C.; PA2 (1) an acrylic resin (e.g., a methyl/butyl methacrylate copolymer); PA2 (2) a carboxylated vinyl resin; and PA2 (3) a moderate chain length epoxy resin; dissolved in PA2 (1) a vinyl chloride/vinyl acetate copolymer having no carboxylic acid groups (e.g., VYHH); PA2 (2) epoxy resin; and PA2 (3) an epoxy hardener, dissolved in; PA2 (1) about 0.6-1.6% by weight phenolic resin; PA2 (2) about 0.8-1.6% by weight acrylic resin; PA2 (3) about 0.4-0.8% by weight polyurethane resin; PA2 (4) about 1.2-3.5% by weight vinyl chloride/vinyl acetate copolymer; PA2 (5) about 1.0-3.0% epoxy resin; and PA2 (6) about 2.5-4.0% epoxy hardener; dissolved in PA2 (i) about 1-6 parts of at least one thermoplastic polyurethane resin; PA2 (ii) about 2-10 parts of at least one thermoplastic polyester resin; or PA2 (iii) about 1-10 parts of a mixture of at least one thermoplastic polyurethane and at least one thermoplastic polyester resin; PA2 (i) about 1-6 parts of at least one thermoplastic polyurethane resin; PA2 (ii) about 2-10 parts of at least one thermoplastic polyester resin; or PA2 (iii) about 1-10 parts of a mixture of at least one thermoplastic polyurethane resin and at least one thermoplastic polyester resin;
Also, U.S. Pat. No. 4,425,263, which issued to Nazarenko on Jan. 10, 1984, teaches a screen-printable PTF composition useful for making membrane touch switches which consists essentially of:
wherein the weight ratio of resin to solvent is from 0.15 to 0.5:1.
U.S. Pat. No. 4,518,524, which issued to Stoetzer on May 21, 1985, teaches a PTF composition useful as a conductive coating comprising:
U.S. Pat. No. 4,535,012, which issued to Martin on Aug. 13, 1985, teaches a conductive PTF composition useful as solderable printed circuit comprising:
U.S. Pat. No. 4,552,690, which issued to Ikeguchi, et al. on Nov. 12, 1985, teaches a conductive PTF composition comprising:
U.S. Pat. No. 4,564,563, which issued to Martin, et al. on Jan. 14, 1986, teaches a conductive PTF composition useful as a solderable electric circuit comprising:
U.S. Pat. No. 4,595,604, which issued to Martin, et al. on Jun. 17, 1986, teaches a conductive PTF composition useful as solderable and flexible printed circuit boards and membrane key boards comprising:
U.S. Pat. No. 4,595,605, which issued to Martin, et al. on Jun. 17, 1986, teaches a conductive PTF composition useful as solderable and flexible printed circuit boards and membrane key boards comprising:
U.S. Pat. No. 4,595,606, which issued to St. John, et al. on Jun. 17, 1986, teaches conductive PTF compositions useful for application to printed circuit boards consisting essentially of:
All of the above-noted U.S. patents are incorporated herein by reference in their entirety.
Ideally, a thermoplastic PTF composition should possess the following combination of properties:
The thermoplastic PTF compositions of the present invention are believed to have this desired combination of properties.